Electronic identification systems typically comprise two devices which are configured to communicate with one another. Preferred configurations of the electronic identification systems are operable to provide such communications via a wireless medium.
One such configuration is described in U.S. patent application Ser. No. 08/705,043, filed Aug. 29, 1996, assigned to the assignee of the present application and incorporated herein by reference. This application discloses the use of a radio frequency (RF) communication system including communication devices. The disclosed communication devices include an interrogator and a transponder, such as a tag or card.
Such communication systems can be used in various identification functions and other applications. The interrogator is configured to output a polling signal which may comprise a radio frequency signal including a predefined code. The transponders of such a communication system are operable to transmit an identification signal responsive to receiving an appropriate command or polling signal. More specifically, the appropriate transponders are configured to recognize the predefined code. The transponders receiving the code subsequently output a particular identification signal which is associated with the transmitting transponder. Following transmission of the polling signal, the interrogator is configured to receive the identification signals enabling detection of the presence of corresponding transponders.
Such communication systems are useable in identification applications such as inventory or other object monitoring. For example, a remote identification device is attached to an object of interest. Responsive to receiving the appropriate polling signal, the identification device is equipped to output an identification signal. Generating the identification signal identifies the presence or location of the identification device and the article or object attached thereto.
It is preferred to maximize communication range between communication devices of the identification system while providing robust communications. Increasing the range also increases the applications of the identification system. Providing robust communications ensures reliability and integrity of the system.
However, limitations exist upon the wireless communication components utilized within the communication devices. For example, given the nature of use of such electronic devices (i.e., attachment of the transponder to other devices or objects), it is preferred to minimize the size of the electronic device. Compact electronic devices also have cosmetic and utilitarian advantages over larger conventional communication devices. Size limitations impose limitations upon the wireless communication components themselves. In addition, the Federal Communication Commission also imposes power limits upon the wireless communication components.
Therefore, it is desirable to provide an identification device which achieves the benefits of increased range and robust wireless communications in consideration of size and power limitations.